This invention pertains to the extrusion of ethylene oxide resin and more particularly to the extrusion of films, pipes, tubings, rods, filaments and other articles from normally solid ethylene oxide polymer compositions using water as an extrusion aid. In addition it also pertains to the use of certain of the so extruded products for packaging materials and dispensing them in water.
At the present there are two methods of preparing poly(ethylene oxide) film, viz., a calendering process or solvent casting. Both of these methods are expensive because of the equipment used in the former process and of the time required in the latter process. Furthermore maintenance of calendering rolls is a tedious chore requiring extraordinary steps to prevent scoring or marring of the calendar rolls surface. In the case of calendering the obtainment of films of uniform thickness is also a problem due to problems encountered with poly(ethylene oxide) resins. For example this resin is subject to chain scission and oxidative degradation.
While the extrusion of poly(ethylene oxide) has been reported, this method had not been hitherto commercial. Since polymers of ethylene oxide have high melt strength and very high melt viscosity, the usual methods known to the art of dealing with these problems are to raise the stock temperature or reduce the back pressure by die design. Polymers of ethylene oxide degrade very rapidly at elevated temperatures both in air and inert environments. Die modifications can be successfully employed for heavy wall sectioned articles but this approach is, e.g., not useful for producing high quality thin gauge film. Although novel and unusual extrusion conditions such as low extrusion temperature coupled with low back pressure have been cited, this has not proved to be reliable. It has at best limited utility and does not appear generally applicable by those skilled in the art. Thus, for example Canadian No. 722,109 describes a process for the dry extrusion of ethylene oxide polymers but this was accomplished by the use of low resistance or low pressure drop film dies which do not give as acceptable an extruded product as the high pressure drop dies used both in the instant invention and preferred by those currently skilled in the art. The high pressure dies afford a more uniform product, by virtue of their spiral configuration, than the low pressure dies which are characterized by having a simple straight, non-spiral die configuration. It should be noted that the pressures reported in Canadian No. 722,109 are "die pressures" and not the maximum extruder pressures often referred to as "head pressures" which are much higher than the former. Thus, for example, while the die pressures reported in Canadian No. 722,109 at page 15 are of the order of 1800 psi, the head pressures are of the order of about 5000 psi. It is the high head pressure encountered in extruding ethylene oxide polymers which has been the stumbling block in the commercial development of these resins. The extrusion of unmodified poly(ethylene oxide) at practical flow rates produces head pressures which would blow the extruder head of commercially available extrusion equipment and warp their screw drives.